1. Field of the Invention
The present invention relates to an electromagnetic valve control system for controlling two exhaust valves, i.e., main and auxiliary exhaust valves, of an engine so that the auxiliary exhaust valve is opened prior to the main exhaust valve.
2. Description of Prior Art
Intake and exhaust valves of some conventional engines are opened and closed by a camshaft. The camshaft is operatively connected to the crankshaft of the engine, so that the timing of opening and closing the intake and exhaust valves with respect to the angle of the crankshaft cannot be varied as the rotational speed of the engine varies. Since the timing of opening and closing the intake and exhaust valves is adjusted in advance to achieve a high engine efficiency at a particular engine rotational speed, the engine efficiency is lowered when the engine rotates at speeds other than the particular engine rotational speed.
There has been proposed an engine whose intake and exhaust valves are opened and closed under electromagnetic forces produced by electromagnets. The timing of opening and closing the intake and exhaust valves can be varied as the rotational speed of the engine varies, so that the engine can operate with high efficiency at different rotational speeds.
In the proposed engine with the electromagnetic valve control system, the intake and exhaust valves themselves can be opened and closed under relatively small forces. When the exhaust valve is to be opened while the engine is in operation, however, a large force is required to be applied to the exhaust valve since the exhaust valve has to be moved against the pressure developed in the combustion chamber. Therefore, the electromagnet for actuating the exhaust valve is large in size, or the exhaust valve may not be opened due to the lack of a sufficient valve actuating force.
For example, if it is assumed that the pressure in the combustion chamber in the expansion stroke is 5 Kg/cm.sup.2 and the surface area of the exhaust valve which faces the combustion chamber is 8 cm.sup.2, then the electromagnetic force required to open the exhaust valve against the pressure in the combustion chamber is 40 Kg (392N). As the exhaust valve is also required to be accelerated when it is opened, an electromagnetic force of about 80 Kg (784N) must be generated by the electromagnet.